Process for hydrotreating a coal tar stream

ABSTRACT

A process for hydrotreating a coal tar stream is described. A coal tar stream is provided, and the coal tar stream is expanded with an inert gas stream to provide an expanded liquid coal tar stream. The expanded liquid coal tar stream is hydrotreated. The coal tar stream can be reacted with a hydrocarbon solvent before it is expanded.

This application claims the benefit of Provisional Application Ser. No. 61/905,980 filed Nov. 19, 2013, entitled Process for Hydrotreating a Coal Tar Stream.

BACKGROUND OF THE INVENTION

Many different types of chemicals are produced from the processing of petroleum. However, petroleum is becoming more expensive because of increased demand in recent decades.

Therefore, attempts have been made to provide alternative sources for the starting materials for manufacturing chemicals. Attention is now being focused on producing liquid hydrocarbons from solid carbonaceous materials, such as coal, which is available in large quantities in countries such as the United States and China.

Pyrolysis of coal produces coke and coal tar. The coke-making or “coking” process consists of heating the material in closed vessels in the absence of oxygen to very high temperatures. Coke is a porous but hard residue that is mostly carbon and inorganic ash, which is used in making steel.

Coal tar is the volatile material that is driven off during heating, and it comprises a mixture of a number of hydrocarbon compounds. It can be separated to yield a variety of organic compounds, such as benzene, toluene, xylene, naphthalene, anthracene, and phenanthrene. These organic compounds can be used to make numerous products, for example, dyes, drugs, explosives, flavorings, perfumes, preservatives, synthetic resins, and paints and stains. The residual pitch left from the separation is used for paving, roofing, waterproofing, and insulation.

Coal tar includes many contaminants. For many processes, it is desirable to treat a coal stream to remove such contaminants. However, some treatment processes for coal tar insufficiently remove contaminants or produce undesirable results, such as saturated aromatic rings. There is a need to improve treatment of coal tar streams.

SUMMARY OF THE INVENTION

One aspect of the invention involves a process for hydrotreating a coal tar stream. A coal tar stream is provided, and the coal tar stream is expanded with an inert gas stream to provide an expanded liquid coal tar stream. The expanded liquid coal tar stream is hydrotreated.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is an illustration of one embodiment of the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The FIGURE shows one embodiment of a basic coal conversion process 5. A coal feed 10 is sent to a pyrolysis zone 15. Alternatively or additionally, in some processes, a portion of the coal feed 10 is sent to a gasification zone (not shown), where the coal feed is mixed with oxygen and steam and reacted under heat and pressure in the gasification zone to form syngas, which is a mixture of carbon monoxide and hydrogen. The syngas can be further processed using the Fischer-Tropsch reaction to produce gasoline or using the water-gas shift reaction to produce more hydrogen.

In the pyrolysis zone 15, the coal is heated at high temperature, e.g., up to about 2,000° C. (3600° F.), in the absence of oxygen to drive off the volatile components. Coking produces a coke stream 25 and a coal tar stream 20. The coke stream 25 can be used in other processes, such as the manufacture of steel. The coal tar stream 20 from the pyrolysis zone, or coal tar streams from other sources, is subjected to a treatment process to provide a treated stream that can be used in various downstream processes.

To reduce the aromaticity of the coal tar stream 20, the coal tar stream 20 can be sent to a reaction zone 35, where the coal tar stream 20 is reacted with added hydrogen in the presence of a hydrocarbon solvent 30. The reaction zone 35 can be, for instance, a continuous stirred-tank reactor (CSTR), a slurry hydrocracking reactor, or a fixed bed reactor. The hydrocarbon solvent 30 can include, for instance, a petroleum cut or other aromatic-type hydrocarbon. Example reaction conditions include a pressure ranging from about 4.8 MPa (about 700 psig) to about 8.3 MPa (about 1200 psig) and a temperature ranging from about 232° C. (450° F.) to about 371° C. (700° F.). A catalyst such as a Ni/Mo hydrotreating catalyst for heavy feeds, or if S level is low enough a Pt/Al₂0₃ catalyst, can be used in the reaction zone 35, but is not required in all embodiments. The reaction zone 35 produces a liquid coal tar stream 40 that is reduced in aromaticity with respect to the coal tar stream 20.

The liquid coal tar stream 40 is fed to an expansion zone 50. The coal tar stream 40 is expanded with an inert gas stream 45 that is fed into the expansion zone 50. The expansion preferably takes place at high pressure, such as between about 10.3 MPa (about 1500 psi) and about 17.2 MPa (about 2500 psi), with an example range of about 2000 psi (13.8 MPa). Suitable inert gases include, but are not limited to, carbon dioxide, nitrogen, and light hydrocarbons such as CH₄, C₂H₄, C₃H₈, and C₄H₁₀. The inert gas stream 45 provides a vapor phase solvent in the expansion zone 50, and improves solubility of hydrogen in later hydrotreating, making the liquid phase more reactive. The expanded liquid coal tar stream 55 includes the hydrocarbon solvent 30 from the reaction zone 35.

In other processes, the reaction zone 35 can be omitted, and the coal tar stream 20 can be fed into the expansion zone 50. In this arrangement, the expanded liquid coal tar stream would not include the hydrocarbon solvent 30.

The expanded liquid coal tar stream 55 is then hydrotreated in the hydrotreating zone 60. Hydrotreating is a process in which hydrogen gas is contacted with a hydrocarbon stream in the presence of suitable catalysts which are primarily active for the removal of heteroatoms, such as sulfur, nitrogen, and metals from the hydrocarbon feedstock. In hydrotreating, hydrocarbons with double and triple bonds may be saturated. Aromatics may also be saturated. The hydrotreating in the hydrotreating zone 60 preferably takes place at about 4.8 MPa (about 700 psi) to about 8.3 MPa (about 1200 psi), and at a temperature range of about 260 C (about 500 F) to about 370 C (about 700 F), a liquid hourly space velocity of about 0.5 hr⁻¹ to about 4 hr⁻¹, and a hydrogen rate of about 168 to about 1,011 Nm³/m³ oil (1,000-6,000 scf/bbl). Conditions can vary depending on the solvent.

The hydrogenation can take place in the presence of a catalyst. Typical hydrotreating catalysts include at least one Group VIII metal, preferably iron, cobalt and nickel, and at least one Group VI metal, preferably molybdenum and tungsten, on a high surface area support material, preferably alumina. Other typical hydrotreating catalysts include zeolitic catalysts, as well as noble metal catalysts where the noble metal is selected from palladium and platinum. Hydrotreating can include hydrodesulfurization, hydrodenitrogenation, or both.

The resulting hydrotreated stream 65 provides a pre-treated stream that can be subject to a processing zone 70 to provide one or more products 75. This pre-treated stream can be relatively free of contaminants such as sulfur and nitrogen. Example hydrotreated streams 65 have a sulfur content of about 50 ppm or less, and a nitrogen content of about 10 ppm or less. Hydrotreating, reaction, and/or expansion conditions can be tuned to provide a desirable decontamination of the coal tar stream 40.

The processing zone 70 can process the hydrotreated stream 65 by hydrocracking, fluid catalytic cracking, alkylation, transalkylation, oxidation, hydrogenation, or a combination of such processes. The hydrotreated stream 65 can also be blended in fuel.

The hydrotreated stream 65 may be fractionated. Alternatively, the coal tar stream 20, 40 may be fractionated before treatment. Coal tar comprises a complex mixture of heterocyclic aromatic compounds and their derivatives with a wide range of boiling points. The number of fractions and the components in the various fractions can be varied as is well known in the art. A typical separation process involves separating the coal tar into four to six streams. For example, there can be a fraction comprising NH3, CO, and light hydrocarbons, a light oil fraction with boiling points between 0° C. and 180° C., a middle oil fraction with boiling points between 180° C. to 230° C., a heavy oil fraction with boiling points between 230 to 270° C., an anthracene oil fraction with boiling points between 270° C. to 350° C., and pitch.

The light oil fraction contains compounds such as benzenes, toluenes, xylenes, naphtha, coumarone-indene, dicyclopentadiene, pyridine, and picolines. The middle oil fraction contains compounds such as phenols, cresols and cresylic acids, xylenols, naphthalene, high boiling tar acids, and high boiling tar bases. The heavy oil fraction contains benzene absorbing oil and creosotes. The anthracene oil fraction contains anthracene. Pitch is the residue of the coal tar distillation containing primarily aromatic hydrocarbons and heterocyclic compounds.

Hydrocracking is a process in which hydrocarbons crack in the presence of hydrogen to lower molecular weight hydrocarbons. Typical hydrocracking conditions may include a temperature of about 290° C. (550° F.) to about 468° C. (875° F.), a pressure of about 3.5 MPa (500 psig) to about 20.7 MPa (3000 psig), a liquid hourly space velocity (LHSV) of about 1.0 to less than about 2.5 hr−1, and a hydrogen rate of about 421 to about 2,527 Nm3/m3 oil (2,500-15,000 scf/bbl). Typical hydrocracking catalysts include amorphous silica-alumina bases or low-level zeolite bases combined with one or more Group VIII or Group VIB metal hydrogenating components, or a crystalline zeolite cracking base upon which is deposited a Group VIII metal hydrogenating component. Additional hydrogenating components may be selected from Group VIB for incorporation with the zeolite base.

Fluid catalytic cracking (FCC) is a catalytic hydrocarbon conversion process accomplished by contacting heavier hydrocarbons in a fluidized reaction zone with a catalytic particulate material. The reaction in catalytic cracking is carried out in the absence of substantial added hydrogen or the consumption of hydrogen. The process typically employs a powdered catalyst having the particles suspended in a rising flow of feed hydrocarbons to form a fluidized bed. In representative processes, cracking takes place in a riser, which is a vertical or upward sloped pipe. Typically, a pre-heated feed is sprayed into the base of the riser via feed nozzles where it contacts hot fluidized catalyst and is vaporized on contact with the catalyst, and the cracking occurs converting the high molecular weight oil into lighter components including liquefied petroleum gas (LPG), gasoline, and a distillate. The catalyst-feed mixture flows upward through the riser for a short period (a few seconds), and then the mixture is separated in cyclones. The hydrocarbons are directed to a fractionator for separation into LPG, gasoline, diesel, kerosene, jet fuel, and other possible fractions. While going through the riser, the cracking catalyst is deactivated because the process is accompanied by formation of coke which deposits on the catalyst particles. Contaminated catalyst is separated from the cracked hydrocarbon vapors and is further treated with steam to remove hydrocarbon remaining in the pores of the catalyst. The catalyst is then directed into a regenerator where the coke is burned off the surface of the catalyst particles, thus restoring the catalyst's activity and providing the necessary heat for the next reaction cycle. The process of cracking is endothermic. The regenerated catalyst is then used in the new cycle. Typical FCC conditions include a temperature of about 400° C. to about 800° C., a pressure of about 0 to about 688 kPa g (about 0 to 100 psig), and contact times of about 0.1 seconds to about 1 hour. The conditions are determined based on the hydrocarbon feedstock being cracked, and the cracked products desired. Zeolite-based catalysts are commonly used in FCC reactors, as are composite catalysts which contain zeolites, silica-aluminas, alumina, and other binders.

Alkylation is typically used to combine light olefins, for example mixtures of alkenes such as propylene and butylene, with isobutane to produce a relatively high-octane branched-chain paraffinic hydrocarbon fuel, including isoheptane and isooctane. Similarly, an alkylation reaction can be performed using an aromatic compound such as benzene in place of the isobutane. When using benzene, the product resulting from the alkylation reaction is an alkylbenzene (e.g. toluene, xylenes, ethylbenzene, etc.). For isobutane alkylation, typically, the reactants are mixed in the presence of a strong acid catalyst, such as sulfuric acid or hydrofluoric acid. The alkylation reaction is carried out at mild temperatures, and is typically a two-phase reaction. Because the reaction is exothermic, cooling is needed. Depending on the catalyst used, normal refinery cooling water provides sufficient cooling. Alternatively, a chilled cooling medium can be provided to cool the reaction. The catalyst protonates the alkenes to produce reactive carbocations which alkylate the isobutane reactant, thus forming branched chain paraffins from isobutane. Aromatic alkylation is generally now conducted with solid acid catalysts including zeolites or amorphous silica-aluminas

The alkylation reaction zone is maintained at a pressure sufficient to maintain the reactants in liquid phase. For a hydrofluoric acid catalyst, a general range of operating pressures is from about 200 to about 7100 kPa absolute. The temperature range covered by this set of conditions is from about −20° C. to about 200° C. For at least alkylation of aromatic compounds, the temperature range is about from 100-200 C at the pressure range of about 200 to about 7100 kPa.

Transalkylation is a chemical reaction resulting in transfer of an alkyl group from one organic compound to another. Catalysts, particularly zeolite catalysts, are often used to effect the reaction. If desired, the transalkylation catalyst may be metal stabilized using a noble metal or base metal, and may contain suitable binder or matrix material such as inorganic oxides and other suitable materials. In a transalkylation process, a polyalkylaromatic hydrocarbon feed and an aromatic hydrocarbon feed are provided to a transalkylation reaction zone. The feed is usually heated to reaction temperature and then passed through a reaction zone, which may comprise one or more individual reactors. Passage of the combined feed through the reaction zone produces an effluent stream comprising unconverted feed and product monoalkylated hydrocarbons. This effluent is normally cooled and passed to a stripping column in which substantially all C5 and lighter hydrocarbons present in the effluent are concentrated into an overhead stream and removed from the process. An aromatics-rich stream is recovered as net stripper bottoms, which is referred to as the transalkylation effluent.

The transalkylation reaction can be effected in contact with a catalytic composite in any conventional or otherwise convenient manner and may comprise a batch or continuous type of operation, with a continuous operation being preferred. The transalkylation catalyst is usefully disposed as a fixed bed in a reaction zone of a vertical tubular reactor, with the alkylaromatic feed stock charged through the bed in an upflow or downflow manner. The transalkylation zone normally operates at conditions including a temperature in the range of about 130° C. to about 540° C. The transalkylation zone is typically operated at moderately elevated pressures broadly ranging from about 100 kPa to about 10 MPa absolute. The transalkylation reaction can be effected over a wide range of space velocities. That is, volume of charge per volume of catalyst per hour; weight hourly space velocity (WHSV) generally is in the range of from about 0.1 to about 30 hr−1. The catalyst is typically selected to have relatively high stability at a high activity level.

Oxidation involves the oxidation of hydrocarbons to oxygen-containing compounds, such as aldehydes. The hydrocarbons include alkanes, alkenes, typically with carbon numbers from 2 to 15, and alkyl aromatics, Linear, branched, and cyclic alkanes and alkenes can be used. Oxygenates that are not fully oxidized to ketones or carboxylic acids can also be subjected to oxidation processes, as well as sulfur compounds that contain —S—H moieties, thiophene rings, and sulfone groups. The process is carried out by placing an oxidation catalyst in a reaction zone and contacting the feed stream which contains the desired hydrocarbons with the catalyst in the presence of oxygen. The type of reactor which can be used is any type well known in the art such as fixed-bed, moving-bed, multi-tube, CSTR, fluidized bed, etc. The feed stream can be flowed over the catalyst bed either up-flow or down-flow in the liquid, vapor, or mixed phase. In the case of a fluidized-bed, the feed stream can be flowed co-current or counter-current. In a CSTR the feed stream can be continuously added or added batch-wise. The feed stream contains the desired oxidizable species along with oxygen. Oxygen can be introduced either as pure oxygen or as air, or as liquid phase oxididents including hydrogen peroxide, organic peroxides, or peroxy-acids. The molar ratio of oxygen (O2) to alkane can range from about 5:1 to about 1:10. In addition to oxygen and alkane or alkene, the feed stream can also contain a diluent gas selected form nitrogen, neon, argon, helium, carbon dioxide, steam or mixtures thereof. As stated, the oxygen can be added as air which could also provide a diluent. The molar ratio of diluent gas to oxygen ranges from greater than zero to about 10:1. The catalyst and feed stream are reacted at oxidation conditions which include a temperature of about 300° C. to about 600° C., a pressure of about 101 kPa to about 5,066 kPa and a space velocity of about 100 to about 100,000 hr−1.

Hydrogenation involves the addition of hydrogen to hydrogenatable hydrocarbon compounds. Alternatively, hydrogen can be provided in a hydrogen-containing compound with ready available hydrogen, such as tetralin, alcohols, hydrogenated naphthalenes, and others via a transfer hydrogenation process with or without a catalyst. The hydrogenatable hydrocarbon compounds are introduced into a hydrogenation zone and contacted with a hydrogen-rich gaseous phase and a hydrogenation catalyst in order to hydrogenate at least a portion of the hydrogenatable hydrocarbon compounds. The catalytic hydrogenation zone may contain a fixed, ebulated or fluidized catalyst bed. This reaction zone is typically at a pressure from about 689 k Pa gauge (100 psig) to about 13790 k Pa gauge (2000 psig) with a maximum catalyst bed temperature in the range of about 177° C. (350° F.) to about 454° C. (850° F.). The liquid hourly space velocity is typically in the range from about 0.2 hr−1 to about 10 hr−1 and hydrogen circulation rates from about 200 standard cubic feet per barrel (SCFB) (35.6 m3/m3) to about 10,000 SCFB (1778 m3/m3).

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims. 

What is claimed is:
 1. A process comprising: providing a coal tar stream; expanding the coal tar stream with an inert gas stream to provide an expanded liquid coal tar stream; and hydrotreating the expanded liquid coal tar stream.
 2. The process of claim 1 wherein hydrotreating the expanded liquid coal tar stream comprises subjecting the expanded liquid coal tar stream to hydrodesulfurization, or hydrodenitrogenation, or both.
 3. The process of claim 1 further comprising: processing the hydrotreated stream by one or more of hydrocracking, fluid catalytic cracking, alkylation, transalkylation, oxidation, and hydrogenation to provide at least one product.
 4. The process of claim 1 wherein the inert gas is selected from the group consisting of carbon dioxide, nitrogen, and light hydrocarbons.
 5. The process of claim 1, wherein the hydrotreating takes place at a temperature range of about 260° C. (about 500° F.) to about 370° C. (about 700° F.).
 6. The process of claim 1, wherein the hydrotreating takes place at a pressure range of about 4.8 MPa (about 700 psi) to about 8.3 MPa (about 1200 psi).
 7. The process of claim 1, wherein the hydrotreating takes place in the presence of a catalyst.
 8. The process of claim 1 further comprising: feeding the coal tar stream and a hydrocarbon solvent into a reaction zone; reacting the coal tar stream and the hydrocarbon solvent in the reaction zone to provide a liquid coal tar stream; and wherein expanding the coal tar stream comprises expanding the liquid coal tar stream.
 9. The process of claim 8 wherein the hydrocarbon solvent comprises an aromatic hydrocarbon.
 10. The process of claim 8 wherein the coal tar stream and the hydrocarbon solvent are reacted at a pressure ranging from about 4.8 MPa (about 700 psig) to about 8.3 MPa (about 1200 psig).
 11. The process of claim 1 wherein providing the coal tar stream comprises pyrolyzing a coal feed into at least the coal tar stream and a coke stream.
 12. A process comprising: providing a coal tar stream; feeding the coal tar stream and a hydrocarbon solvent into a reaction zone; reacting the coal tar stream and the hydrocarbon solvent in the reaction zone to provide a liquid coal tar stream; and expanding the reacted coal tar stream with an inert gas stream to provide an expanded liquid coal tar stream; and hydrotreating the expanded liquid coal tar stream.
 13. The process of claim 12, wherein the hydrotreating takes place at a temperature range of about 260° C. (about 500° F.) to about 370° C. (about 700° F.) and a pressure range of about 4.8 MPa (about 700 psi) to about 8.3 MPa (about 1200 psi).
 14. The process of claim 12 wherein the inert gas is selected from the group consisting of carbon dioxide, nitrogen, and light hydrocarbons.
 15. The process of claim 12 wherein hydrotreating the expanded liquid coal tar stream comprises subjecting the expanded liquid coal tar stream to hydrodesulfurization, or hydrodenitrogenation, or both.
 16. The process of claim 12 further comprising: processing the hydrotreated stream by one or more of hydrocracking, fluid catalytic cracking, alkylation, transalkylation, oxidation, and hydrogenation to provide at least one product.
 17. The process of claim 12, wherein the hydrotreating takes place in the presence of a catalyst.
 18. The process of claim 12 wherein the hydrocarbon solvent comprises an aromatic hydrocarbon.
 19. The process of claim 12 wherein the coal tar stream and the hydrocarbon solvent are reacted at a pressure ranging from about 4.8 MPa (about 700 psig) to about 8.3 MPa (about 1200 psig).
 20. The process of claim 12 wherein providing the coal tar stream comprises pyrolyzing a coal feed into at least the coal tar stream and a coke stream. 